| Reseaches on hillslope soil erosion characteristics in the Northeast black soil region may provide important theoretical basis for erosion control and sustainable utilization of black soil.Based on the reseach weakness and gap about key driving factors in black soil region,this dissertation used the field observation and laboratory simulation experiments to investigate hillslope soil erosion characteristics under free drainage?FD?and artesian seepage?AS?near-surface soil hydrologic conditions in the Chinese black soil region.The effects of upslope runoff and sediment on downslope erosion processes were analyzed;the characterisctics of soil detachment and deposition distribution along hillslipe under both FD and AS conditions were revealed;the hydrodynamic mechanisms of hillslope soil eroiosn under the FD and AS conditions were discussed.The main results were as follows:?1?The effects of raindrop impact on hillslope soil erosion in the Chinese black soil region were discussed.Compared with the treatments without raindrop impact,soil erosion rate under both FD and AS conditions significantly increased by 2.7–7.0 and 1.7–3.4 times,respectively.The contributions of raindrop impact to soil erosion rate at the FD and AS conditions were 72.7%–87.4% and 42.4%–70.5%,respectively.The contributions of artesian seepage to soil loss with and without raindrop impact were 20.8%–69.3% and 54.9%–85.5%,respectively;while the contribution of artesian seepage to soil loss without raindrop impact was greater than that with raindrop impact.Compared with the FD conditions,flow velocity,Reynolds number and Froude number under the AS conditions increased by 17.5%–33.5%,27.4%–58.4% and 12.9%–25.9%,respectively;while Darcy-Weisbach resistance coefficient decreased by 21.5%–37.1% under AS conditions.?2?The influences of rainfall intensity on hillslope soil loss in the Chinese black soil region were analyzed.With an increase in rainfall intensity,runoff rate and soil erosion rate significantly increased under both near-surface soil hydrologic conditions.While soil erosion rate under the AS condition were 1.7–3.6 times higher than that under the FD condition.The contributions of artesian seepage to soil loss under 50 and 100 mm h-1 rainfall intensities were 41.3%–72.4% and 50.8%–69.3%,respectively.With an increase in rainfall intensity,flow velocity,Reynolds number and Froude number obviously increased;while Darcy-Weisbach resistance coefficient decreased.Compared with the FD condition,flow velocity,Reynolds number and Froude number under the AS condition increased by 17.5%–33.5%?27.4%–58.4% and 12.9%–25.9%,respectively;while Darcy-Weisbach resistance coefficient decreased by 21.5%–37.1% under the AS condition.?3?The impacts of slope gradient on hillslope soil loss in the Chinese black soil region were studied.Runoff rate,soil erosion rate and sediment concentration were increased with increasing slope gradient under both FD and AS conditions.The contributions of artesian seepage to soil loss under 2.5° and 5° were 41.3%–72.4% and 50.8%–69.3%,respectively.Under both FD and AS conditions,flow velocity,Reynolds number and Froude number increased with increasing slope gradient;while Darcy-Weisbach resistance coefficient decreased.?4?The characteristics of detachment-deposion distribution within 5 m slope length under both FD and AS conditions were discussed.At 2.5° treatments,when slope length increased,sediment regime changed from detachment-transport dominated to detachment-deposition dominated under the FD condition.When slope gradient increased to 5° and 10°,sediment regime changed from detachment-deposition dominated to detachment-transport dominated with increasing rainfall intensity.Under the AS condition,at 2.5° treatment,sediment regime changed from detachment-deposition dominated to detachment-transport dominated with increasing rainfall intensity.When slope gradient increased to 5°,sediment regime changed to detachment-transport dominated within 5 m slope length;the net sediment yield within 5 m slope length increased 1.7–8.2 times with increasing rainfall intensity.?5?Upsloe runoff and sediment influences on downslope soil detachment-deposion process were quantitatively described.As rainfall intensity and slope gradient increased,Sd and Sud increased under both FD and AS conditions;while it showed different increasing trends under both near-surface soil water hydrological conditions.Under 2.5° and 5° at 50 mm h-1 rainfall intensity treatments,when upslope runoff increased,sediment regime changed from detachment-transport dominated to detachment-deposition dominated under the FD condition;while under 5° at 100 mm h-1 rainfall intensity treatment,sediment regime was detachment-transport dominated.After eliminating raindrop impact,sediment regime caused by upslope runoff and sediment was detachment-deposition dominated.The relations between the downslope soil loss caused by upslope runoff and sediment concentration were established under both FD and AS conditions.Impacts of upslope runoff and sediment on downslope erosion process were dependent on upslope runoff,sediment concentration,rainfall intensity and slope gradient.?6?The flow hydrodynamic mechanisms of hillslope soil erosion under both FD and AS conditions were clarified.The relational expressions between soil erosion per unit width and shear stress,stream power,and unit stream power under the FD and AS conditions were established,respectively.The results showed that compared with the FD treatment,the critical shear stress,the critical stream power,and the critical unit stream power of soil erosion under the AS condition decreased by 10.3%,19.2% and 14.7%,respectively.Furthermore,under both FD and AS conditions,the stream power was the best flow hydrodynamic parameter for quantifying hillslope soil erosion in the Chinese Black soil region. |
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